LONDON - U.S. stocks tumbled, extending the biggest weekly drop of the year for the Standard & Poor’s 500 Index, after data showed the nation added less than half the number of jobs economists forecast in March.

Bank of America Corp. and Citigroup Inc. fell more than 1.6 percent as financial shares slumped. Caterpillar Inc. and General Electric Co. slid at least 1.1 percent to pace declines among the largest companies. F5 Networks Inc. tumbled 19 percent after lowering its revenue forecast. Cisco Systems Inc. and Juniper Networks Inc., the makers of communications equipment, lost more than 3.6 percent.

The S&P 500 retreated 1.1 percent to 1,542.2 at 9:43 a.m. in New York. The equity benchmark gained 0.4 percent yesterday as Japan’s central bank increased its stimulus program. It is down 1.7 percent for the week. The Dow Jones Industrial Average fell 140.39 points, or 1 percent, to 14,465.72 today. Trading among S&P 500 shares was 27 percent above the 30-day average at this time of day.

“This report is a huge disappointment,” Mark Luschini, chief investment strategist at Philadelphia-based Janney Montgomery Scott LLC, which oversees $55 billion, said in a telephone interview. “This will spook the market and it obviously means that the Fed will remain on vigil with regards to the highly accommodative monetary policy.”

Payrolls grew by 88,000 workers last month, the smallest in nine months, after a revised 268,000 gain in February that was higher than first estimated, Labor Department figures showed today in Washington. The median forecast of 87 economists surveyed by Bloomberg projected an advance of 190,000. The jobless rate fell to 7.6 percent from 7.7 percent.

‘Good day’

“The number is disappointing and moderately concerning, but one month does not make a trend,’’ David Roda, the Miami- based regional chief investment officer for Wells Fargo Private Bank, said in a phone interview. His firm manages $170 billion. “Yes, it’s a miss and it’s worth focusing on but we don’t think it changes our forecast for a modest improvement in employment this year. It’s a good day to buy stocks because it made the markets nervous.”

The bull market in U.S. equities entered its fifth year last month. The S&P 500 has surged 128 percent from a 12-year low in 2009 as companies reported better-than-estimated earnings and the Federal Reserve embarked on three rounds of bond purchases to stimulate the economy. The S&P 500 and the Dow closed at record highs on April 2.

Alcoa Inc. unofficially kicks off the first-quarter earnings season on April 8 when it reports its financial results after equity markets close.

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